1. Field of the Invention
The present invention relates to a magnetic disk drive device, and in particular, to a pseudo contact type negative pressure air bearing slider for a transducer head assembly of a magnetic disk drive device.
2. Description of the Related Art
Transducer head assemblies have been designed to literally fly over a rapidly rotating disc, and include an air bearing slider for carrying a magnetic transducer proximate a rapidly rotating disc. The transducer, in the case of pseudo contact type sliders, is generally a thin-film head.
Computer disk drive technology evolution has focused on improvements in “areal density”, or the number of bits of information that can be stored in a given space on a magnetic disk. Over the last decade, the majority of progress has been gained through miniaturization of the recording heads and improving the magnetic efficiency of the write/read elements in the heads, and similar improvements in the magnetic and physical properties of the disks.
As suggested above, disk drives contain a plurality of recording heads that “fly” over rotating disks. The magnetic recording efficiency is a function of many physical characteristics of the heads and disks, the most significant of which is the spacing between the rotating disk surface and the recording head “pole” elements. The most straightforward method for manufacturers to improve areal density has been to reduce the spacing between the head disk, without sacrificing the long term reliability of the disk drive.
Across the previous disk drive industry product offerings, head-disk spacing had steadily decreased from several micro-inches to less than two micro-inches, until there came a point that further increases in areal density required the head to essentially touch the disk during flying. A new class of so-called “pseudo-contact” heads were developed in which the rear portion of the head, where the transducer poles are located, is in constant contact with the disk surface. Various design characteristics were developed to minimize friction and wear between the disk and head, and such “pseudo-contact” designs have proven to be as reliable over the long-term as the non-contact designs.
In magnetic disk technologies, it is generally desired to achieve higher data recording densities without a substantial change in form factor. In the context of the air bearing slider, increased recording densities are obtainable by maintaining the flying height, pitch angle and roll angle constant over the whole disk surface, to thereby enhance floating stability and contact start stop (CSS) reliability. In the case of the pseudo contact type slider, the “flying height” of the slider in effect refers to the pressure (or lack of pressure) applied to the disk surface by the assembly, and in particular, by the thin film transducer. Ideally, the slider should fly at a height in which the transducer makes pseudo contact with the disk surface at minimum pressure.
On the one hand, the magnetic head must fly at a sufficient height to avoid frictionally related problems caused by excessive physical contact during data communication between the magnetic head and the rapidly rotating disk. On the other hand, the head should be made to fly as low as possible to obtain the highest possible recording densities. As the magnetic head is fixed to the slider mechanism, the disk recording density increases as the flying height of the slider decreases. Accordingly, it is preferred that the slider fly as close as possible to the disk surface. A constant flying height is preferably maintained, regardless of variations in tangential velocity during flying, cross movements of the slider during data search operations, and changes in skew angle in the case of rotary type actuators.
To achieve stable flying characteristics, the slider should also fly at a pitch angle that falls within a safe range of a predetermined value. The pitch angle is defined as the tilt angle between the principal plane of the slider in the tangential direction of the rotating disc and the principal plane of the disc surface. The pitch angle is positive in the normal case in which the flying height of the rear portion of the slider is lower than that of the front portion of the slider. A transducer is generally situated at the lowest position of the rear portion of the slider for maximizing recording data capacity. If the designed pitch angle is too small, the possibility exists that a disturbance will cause the front end of the slider to dip down such that a negative pitch ensues resulting in a collision with the rapidly rotating disk. On the other hand, if the designed pitch angle is too large, the air stiffness needed for stable flying can be disadvantageously reduced. Therefore, to maintain stability while avoiding the situation of a negative pitch angle, the slider should be configured such that the pitch angle can be controlled to fall within an optimum value range. Another factor to consider regarding pitch angle is the general tendency for the pitch angle to increase with skew angle increases as the slider is positioned in a radially outward direction over the disc surface. Thus, the pitch angle should fall within the safe range regardless of skew angle variations.
Differing hydrodynamic forces support the inner and outer air bearing surface (ABS) rails of the slider, and resulting variations in side leakage air flow with skew angle changes can generate roll angle variations. Here, the inner and outer rails refer to those ABS rails of the slider positioned toward the inner periphery and outer periphery of the disc, respectively. Also, roll angle is defined as the tilt angle between the principal plane of the slider in the radial direction of the disc and the principal plane of the disc surface. As the transducer is usually centrally located on the rear slider edge in the case of pseudo contact slider, optimum performance is obtained by avoiding roll angle over the entire disk surface area.
FIG. 1 is a schematic perspective view of a conventional tapered flat slider. In FIG. 1, two rails 11a are formed in parallel at a predetermined height on a surface of a slim hexahedron body 10a to thus form lengthwise extending ABS's. A tapered or sloped portion 12a is formed at each leading edge portion of the ABS rails 11a. In such a structure, air within a very thin boundary layer rotates together with the rotation of the disk due to surface friction. When passing between the rotating disk and the slider, the air is compressed by the ramp 12a on the leading edge of the ABS 11a. This pressure creates a hydrodynamic lifting force at the ramp section which is sustained through the trailing edge of the ABS, thus allowing the slider to fly without contacting the disk surface.
The conventional slider of this type suffers a drawback in that the flying height, pitch angle and roll angle vary considerably according to the skew angle of the rotary type actuator, i.e., according to the radial position of the slider over the disc surface. For flying heights of 3.0 millionths of an inch and greater, minor height and tilt fluctuations in the slider do not generally affect the read/write operations of the disk. However, current-day standards require flying heights below 2.0 millionths of an inch. At such small flying heights, even minor variations in flying height, pitch angle and roll angle can severely affect the reliability of the head read/write function of a hard disk drive.
An improved configuration aimed at countering flying height variations over the entire disc surface is the transverse pressure contour (TPC) slider, as described, for example, in U.S. Pat. No. 4,673,996. As shown in FIG. 2 herein, this slider is also characterized by ABS rails 11b formed on a slider body 10b, and ramp portions 12b formed at the leading edge of the ABS rails 11b. In addition, however, a step-down 111b is formed lengthwise on the both sides of each of the ABS rails 11b. The slider of this TPC structure has the advantage of maintaining reasonably constant flying height regardless of skew angle variations. However, this TPC slider exhibits reduce  reduced flying stability which is caused by insufficient air stiffness resulting in the reduction of the ABS surface area. Also, the TPC modification does not improve pitch and roll angle variations resulting from changes in skew angle.
In light of the above, to better realize a constant flying height and constant pitch and roll angles and to obtain an improve contact start stop (CSS) performance, most current air bearing sliders have adopted a negative pressure air bearing (NPAB) type of configuration with a variety of air bearing surface shape changes. A basic NPAB slider has the same structure of the slider shown in FIG. 1, together with a cross rail connecting the ABS rails. That is, as shown in FIG. 3, two ABS rails 11c each having a slope 12c at a leading edge thereof are formed in parallel on a surface of a body 10c. A cross rail 13c having the same height as the ABS rail 11c is formed between the rails 11c proximate the slopes 12c. The cross rail 13c creates a negative pressure cavity 14c  15c in proximity to the central surface portion of the body 10c. Thus, since the pressure of the air passing over the cross rail is diffused as it passes the negative pressure cavity 14c  15c, a pulling or suction force is downwardly applied on the slider which reduces suspension gram load and provides the advantage of a fast take off from the disc surface. The counter action between the positive and negative forces reduces the sensitivity of the slider flying height relative to disc velocity and increases the slider stiffness characteristics.
Because of sub-ambient pressure of cavity 14c  15c, roll angle during a high skew condition can worsen, meaning that the NPAB slider of FIG. 3 exhibits more negative roll effects at high skew positions than the convention tapered flat slider of FIG. 1. Also, there is a tendency for debris to gather at the cross-rail 13c. Such debris can ultimately have an adverse effect on performance.